Technical Abstract:
Corn can become contaminated with aflatoxin if it is infected by the fungus, Aspergillus flavus during the grain development and drying or in storage if not sufficiently dried. While A. flavus is thought of as a ‘weak’ pathogen, efforts to prevent infection have not been entirely successful. Genetically modified corn expressing insecticidal Bt proteins have reduced some opportunistic fungal diseases, but have not reliably prevented A. flavus infection. Breeding for resistance to A. flavus infection has not yielded any commercially acceptable hybrids. Similarly, tillage, irrigation and fertility management practices cannot consistently reduce aflatoxin concentrations. At present, the best approach to prevent aflatoxin contamination of corn is through biological control.
Some naturally-occurring isolates of A. flavus do not produce aflatoxin. These non-toxigenic isolates can be applied in corn fields to compete with the toxigenic isolates. The corn may still become infected with A. flavus, but will have zero or reduced levels of aflatoxin. Research to date has focused on three non-toxigenic strains of A. flavus: a Georgia isolate from peanut, which has been commercialized for corn and peanut as Afla-Guard®; an Arizona isolate, AF36 from cotton, and a USDA-licensed, Mississippi corn isolate, K49.
Strain K49 has been tested in the Mississippi Delta for over 10 years. This area has become a significant corn-producing region but has more common problems with aflatoxin contamination than the Corn Belt, because of the persistent heat, humidity and insect pressure. Also, while the Mississipi Delta has increased corn production the on-farm storage capacity has lagged. Most grain bins do not have dryers and some corn is stored in polyethyelene silobags or even in covered piles on the ground.
Experiments are underway by the USDA-ARS Biological Control of Pests Research Unit to learn: 1) How persistent are deployed biological control strains in the agroecosystem. 2) What are the mechanisms for successful biological control of A. flavus. 3) What are the most effective methods for deploying strain of A. flavus.